This type of drainage unit may be used whenever the appearance of a leak in a hydraulic circuit may lead to unacceptable consequences for the environment. In particular, this situation may occur when the hydraulic fluid circulating in the circuit is a danger itself or dangerous owing to chemical or explosive reactions causing said fluid to escape outside the circuit. This situation may also occur if the hydraulic circuit is situated immediately close to an electric or electronic installation.
This latter situation applies in particular to the drinking water distribution circuit on aircraft. In fact, any possible leaking from this circuit must in no instance result in a flowing of water towards the electronic and electric systems located close to certain sensitive zones of the circuit.
So as to eliminate this risk, it is normal to add to the aircraft drinking water circuit, certainly at least in these sensitive zones close to the electronic and electric systems, drainage circuits disposed around the water distribution pipes. These drainage circuits allow a possible water leak to be drained towards external drains situated in those zones far away from the aircraft electronic and electric systems.
In practice, the drainage circuits are constituted by pipes situated disposed concentrically around the water distribution pipes and by drainage units placed on the enlarged portions of the water circuit and constituted by the righthand, T or Y connectors of this circuit.
When the enlarged portion of the water circuit corresponds to a righthand connector, the drainage unit normally includes a large diameter sheath surrounding the connector and having its extremities being glued onto metallic joining pieces mounted on the water distribution pipes close to the connector, and also supporting the adjacent extremities of the drainage pipes. In this case, imperviousness of the drainage circuit is therefore ensured by glueing the sheath to the joining pieces. As a result, the quality of imperviousness mainly depends on whether or not glueing has been effected carefully. Furthermore, if a leak occurs in the connector, the pressure generally existing in the water circuit favors separation of the sheath and the appearance of a leak in the drainage circuit.
When the widened portion of the water circuit corresponds to a T or Y-shaped connector, the drainage unit normally includes two identical half-shells having opposing flat faces by which said half-shells are glued to each another. These half-shells are also glued onto metallic joining pieces placed as previously on the extremities of the water distribution pipes adjacent to the connector and also used to support the extremities of the drainage pipes. The holding of these half-shells in position is ensured by three metallic rings placed around said metallic joining pieces. Given the fact that the surface evenness of the surfaces opposite the half-shells is rarely satisfactory, imperviousness of these drainage units is difficult to obtain. Moreover, this imperviousness depends on the continuity and thickness of the glue cord and tends to decrease if there is a leak from the connector, having regard to the pressure existing in the water circuit.
The preceding description reveals that the drainage units, currently used in drainage circuits associated with the hydraulic circuits calling for protection from leaks, are not always completely impervious, this imperviousness being difficult to obtain and whose effectiveness tends to diminish by virtue of the pressure existing in the hydraulic circuit when a leak occurs in said circuit.